Apparatus for making magnetic



June 4, 1935. c; HERMANN Re. 19,601

APPARATUS FOR MAKING MAGNETIC TESTS AND MEASUREMENTS Original Filed March 24, 1933 Fig.4.

ITHIH|||IIIIIIIIIHUIIXIIHHIII Inventor": Peter C. Hermann.

is Attorney.

Reiaued June 4, 1935 UNITED STATES APPARATUS FOR MAKING MAGNETIC TESTS AND MEASU'BWTS Peter C. Hermann,

Berlin-Zehlenderl-llltte,

Germany, assignor to General Electric Oompany, a corporation of New York Original No. 1,951,211, dated May 1, 1934, Serial No. 662,804, March 24, 1933.

Application for reissue February 6, 1935, Serial No. 5,211. In

Germany April 6, 1932 7 Claims.

My invention relates to an apparatus for making magnetic tests and measurements and concerns particularly an arrangement suitable for testing different materials under working conditions. The present application relates to an arrangement for utilizing the apparatus disclosed in my copending application, Serial No. 5,276 filed Feb. 6, 1935, assigned to the same assignee as the present application in connection with alternating currents and for making measurements of magnetic loss.

In the laboratory, magnetization curves may readily be determined for the purpose of ascertaining the characteristic magnetic constants such as coercive force, remanence, initial and maximum permeability, hysteresis losses and saturation, and the like. Accurate results may be obtained by carrying out the measurements on a closed ring. The laboratory method utilizing a closed ring, however, is not suitable when the tests are to be carried out under working conditions continuously or when it is desired to take repeated measurements on a piece of sheet metal in order to determine the thermal effects, for example.

The necessity for the use of a closed ring has been overcome in certain types of apparatus by building up cores from test strips arranged in layers in a closed form or by utilizing a closing yoke. However, the accuracy of the apparatus and the uniformity of the, results is interfered with by the presence of the free poles formed at the abutting joints which tend to demagnetize the magnetic material.

It is an object of my invention to provide an apparatus in which the difllculties of the prior devices are overcome by magnetizing the sample in a. coil and taking a direct measurement of the eitective field strength as well as the magnitude of other magnetic conditions in the sample. It is a further object of my invention to provide an apparatus in which tests may be made upon small quantities of test material in shapes that may be obtained easily, particularly fiat strips or sheets.

In accordance with my present invention apparatus of the type disclosed in my copending application above-mentioned, is used in conjunction with means for producing alternating currents and controlling their phase relationship.

In the form of my invention the sample in the form of a strip of sheet metal is surrounded by a magnetizing winding. The'width oi the strip is so great that the effect of any hardening at the edge is negligible. The operation of my device depends upon the principle that the actual eflective field strength in the metal strip is just as great as the field strength in the air at the surface of the metal. This law is based upon the continuity of the tangential component of the field strength when passing to the outside layers.

One or two filamentary conductors are mounted in close proximity to the surface of the test strip and the deflection of the filaments when a current is passed through them provides an indication of the strength of field at the surface of the magnetic test strip. When using the apparatus with alternating currents, means are provided for causing an alternating current to flow through said filament in phase with the magnetic field to which the test strip is subjected. For making less measurements the current through the filament is made proportional to and in phase with the magnetic induction through the test strip. Any suitable means such as a microscope used to observe the motion of the filaments or a rotating mirror carried by the pair of filaments in the manner 0! an oscillograph loop may be employed in conjunction with an optical system in order to provide an indication of the bending of the filaments thereby providing an indication of the strength of field. The features of my invention which I believe to be novel and patentable will be pointed out in the claims appended hereto.

A better understanding itself, however, may be obtained by referring to the i'ollowing description taken in connection with the accompanying drawing in which Fig. 1 is a circuit diagram of one embodiment of my invention; Fig. 2 is a circuit diagram of. a modified arrangement more particularly adapted to measurements taking into consideration the effect of harmonics: Fig. 8 is a cross-sectional view of the apparatus used in connection with the arrangement of Fig. 1; and Fig. 4 is a schematic diagram illustrating the optical circuit of the arrangement shown in Fig. 3 and indicating the apparatus in horizontal longitudinal section.

Referring now more in detail to the drawing in which like reference characters refer to like parts throughout, I provide a cylindrical magnetizing winding ii energized by any suitable source of alternating current, such as an alternator ii. A test piece II is placed in magnetic relation to the magnetizing winding il. Preferably the test piece I! takes the form of a flat strip supported within the winding ii by nonmagnetic trame II.

In order to provide a direct indication of the field strength within and at the surface of the test piece II, a current-conducting filament II is mounted in close proximity to the surface of the test piece ll. Although I am not limited to this specific arrangement, I prefer to employ a pair of parallel filaments l5 and it connected in seties at one end. An alternating current, also supplied if desired by the alternator II, is caused to fiow through the filaments II and I8. Since current flows in opposite directions in the two filaments, they are deflected in opposite directions. A mirror ll supported between filaments l5 and I6 cooperates with a suitable device 20, such as a mirror or prism. a source of light 2| and a suitable device, such as a screen or a scale 22, to provide an indication of the deflection? of the filaments I! and I in response to the reaction between the current flowing in the filaments and a magnetic field at the surface of the test piece I3.

The filaments l5, it are located in a field which is so close to the surface of the magnetic test piece l3 as to be substantially unchanged from the field within the test piece. Consequently the deflection of the filaments i5 and II provides a direct indication of the field strength. In my apparatus, corrections which would have to be made in calculating the field strength from the magnetizing current are therefore rendered unnecessary.

Owing to the fact that the reaction between a current conductor and a magnetic field depends both on the magnitude of the quantities and the phase relationship between them when alternating quantities are involved, it is necessary to fix the phase relationship between the current flowing in filaments l5, l8 and the magnetic field produced by the magnetizing winding ll. Any suitable device such as a phase shifter or a suitable arrangement of variable impedances may be provided for varying the phase relationship. For example, in the arrangement shown in Fig. 1, the alternator I2 is connected to the primary of a controlling circuit through variable resistors II and 28, and a variable coupling transformer 30, forming in conjunction with the resistances a complex compensator, is utilized to transfer the energy from this circuit to the filaments I5 and IS. The ammeter ll serves to indicate the magnitude of the current drawn from the alternator II for the energization of the filaments II and IS. A double-pole, doublethrow switch I! is provided for opening and closing a circuit from the complex compensator 30 to the filaments I! and Ii. The strength of the current is controlled by adjusting the rheostats 28 and 28, and the phase relationship is adjusted by varying the coupling between the primary and secondary windings I3 and II of the transformer 30. By varying the adjustment until the maximum deflection of the mirror I! is obtained, an adjustment results which corresponds to phase uniformity between the current flowing in the filaments II, It and the magnetic field to which the sample II is subjected.

By causing the current flowing in filaments l5 and iii to vary in phase relationship and magnitude with the magnetic induction through the sample l3, my apparatus may also be utilized to obtain an indication of magnetic loss since, as is well known, the magnetic loss in magnetic material is a function of the product of field strength or magnetizing force and flux density or magnetic induction. To this end a tin: measuring coil, preferably divided in two parts 33 and II, is so arranged that it may be connected to the phase compensator ill by throwing the double-pole, double-throw switch 32 to the right. The adjustment of the compensator is then varied until the deflection of the alternating current galvanometer 24 fails to zero thereby indicating that the voltage produced by the compensator is exactly opposed in phase and magnitude to the voltage induced in the induction measuring coils 23 and 25 by the magnetic induction in the sample ii. If the double-pole, double-throw switch 32 is then thrown to the left, the current in the filaments l5 and i6 will correspond in magnitude and phase to the magnetic induction of the sample I! and the deflection of the mirror I! will provide an indication of the product of magnetizing force and induction thereby permitting the apparatus to be calibrated in terms of magnetic loss.

If the apparatus is to be used for making tests with alternating currents containing harmonics or if the test is intended to take in consideration the harmonics in the wave form of the fiux produced by the characteristics of the magnetic material, it is desirable to produce a current in the filaments I5 and i6 which exactly simulates the wave form oi the magnetic induction. For this purpose the apparatus disclosed in Fig. 2 may be utilized in which a three-element discharge tube 35 controls the current in the filaments lli, II in accordance with the voltage induced in induction measuring coils 23 and II.

The discharge tube 35 is provided with a control grid 38, a filamentary cathode 31 and an anode 38. The cathode 31 is energized by a filament battery 81'. The induction measuring coils 2! and 15 are connected in the grid circuit of the discharge tube 35 in series with a grid battery It between the cathode 31 and the control grid 3! so that the potential of the control grid varies with the voltage induced in the induction measurlng coils 23 and 25. The plate circuit of the discharge tube SI contains a source of plate potential and a resistor 4| connected in series between the anode ill and the cathode 31. The filamentary conductors l5 and I! are connected in a circuit which is connected in parallel to the resistor ll so that the current in filaments l5 and I8 varies with the plate current of the discharge tube. It will be understood that the discharge tube is to be operated in the straight portion of its characteristic curve so that the plate current will vary linearly with the grid voltage.

The direct current component of the plate current may be balanced out. if desired, by means of acompensator consisting of potentiometer 42 energized by a battery ll. The portion of the potentiometer 2 between its variable tap N and its terminal 45 and the filaments II, II in series are connected across the resistor 4|. The polarity of the battery I! and the setting of the tap M is such that the direct current component of the plate current is compensated and no current flows in filaments I! and it when the induction in the sample I! and consequently the voltage induced in induction measuring windings 2i and II is zero. Since the plate current in the discharge tube 35 responds with very great rapidity to variations in the grid voltage, the plate current and consequently the current flowing in substantially non-inductive circuit of fll'sments II and It follows the magnetic induction of the sample it however complex its wave form may be. In consequence, the apparatus maybe 1 used for measuring the loss in the samples subiected to magnetizing currents of diflerent wave forms and rgardless of the distortion of the wave form resulting from the characteristics of the material being tested.

In accordance with the provisions of the patent statutes I have described the principle of operation of my invention together with the apparatus which I now consider to represent the best embodiment thereof, but I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. Apparatus for making magnetic measurements of magnetic samples having flat surfaces, comprising an alternating current magnetizing winding, means for supporting such a sample in testing position in magnetic relation with said winding, a flexible current conductor supported so as to be parallel with and in relatively close proximity to the surface of a sample in testing position, and means for supplying to said conductor an alternating current in' phase with a magnetic field in said sample, thereby causing a deflection of said conductor and an indication of the strength of said magnetic fleld in the sample under test.

2. Apparatus for making magnetic measurements of test pieces having fiat surfaces, comprising a magnetizing winding arranged to surround said test piece, means for energizing said winding with alternating current, a pair .of current-conducting filaments connected in series and supported transverse to the axis of said magnetizlng winding so as to be parallel with and in relatively close proximity to the surface of a piece in testing position, said pair of filaments being twisted in accordance with the magnetic field strength to which the test piece is subjected thereby providing a direct response to the strength of said field, and means for causing an alternating current to flow through said conducting filaments in phase with the current energizing said magnetizing winding.

3. Apparatus for making magnetic measurements of magneticsamples having flat surfaces comprising an alternating current magnetizing winding arranged to permit placing such a sample in magnetic relation thereto in testing position, a flexible current conductor supported so as to be parallel with and in relatively close proximity to the surface of a sample in testing position, and means for supplying to said flexible conductor an alternating current and controlling the phase relationship thereof.

4. Apparatus for making magnetic measurements of magnetic samples having fiat surfaces, comprising an alternating current magnetizing winding, means for supporting such a sample in testing position in magnetic relation with said winding, a flexible current conductor supported so as to be parallel with and in relatively close proximity to time surface of a sample in testing position, and a complex compensator for supplying to said conductor an alternating current in phase with the field produced by said magnetis ing winding so as to cause a deflection of said conductor and an indication of the magnitude of a magnetic condition in a sample under test.

5. Apparatus for measuring magnetic loss in magnetic samples having flat surfaces, comprising a magnetizing winding, means for supporting such a sample in testing position in magnetic relation with said winding, a flexible current conductor supported so as to be parallel with and in relatively close proximity to a surface of a sample in testing position, an induction-responsive coil in inductive relation with the sample under test, means associated with said coil for supplying an electrical current to said flexible current conductor varying in phase and magnitude with variations in magnetic induction through said induction-responsive coil whereby said flexible conductor is caused to deflect an amount dependent upon the product of field strength and magnetic induction so as to give an indication of magnetic loss.

8. Apparatus for measuring magnetic loss in magnetic samples, comprising means for subjecting a sample to be tested to an alternating magnetic field, a flexible conductor subjected to a field substantially equal to that within said sample and means for causing a current to flow through said conductor varying in phase and magnitude with the magnetic induction in said sample, whereby said conductor is caused to deflect an amount dependent upon the product of field strength and magnetic induction thereby giving an indication of magnetic loss in said sample.

7. Apparatus for making magnetic measurements of magnetic samples having flat surfaces, comprising a magnetizing winding, means for supporting a sample in testing position in magnetic relation with said winding, 0. flexible current conductor supported so as to be parallel to and in relatively close proximity to the surface of a sample in testing position, an induction measuring coil in magnetic relation with said sample so as to have induced therein a voltage proportional to the magnetic induction in said sample, a three-element discharge tube having a control grid, a source of current energizing said tube, said control grid being connected to said induction measuring coil and said flexible conductor being connected in series with said discharge tube whereby a current is caused to flow through said flexible conductor varying in phase and magnitude with the magnetic induction through said magnetic sample thereby causing said flexible conductor to be deflected an amount dependent upon the product of magnetic induction and field strength to which said sample is subjected.

PETER C. W. 

